The origin of the day's observance lies in the Temple service described in the Mishnah: the kohanim gathered willow branches at Motza and stood them around the altar, circling it once each day of Sukkot but seven times on the seventh day, calling out "Ana Hashem hoshi'a na" (Sukkah 45a:2-3), a practice further detailed by Rav Eliezer Melamed (Peninei Halakhah, Sukkot 5:9) and rooted in the words of Tehillim 118:25.
The Rambam explains that after the Temple's destruction the aravah, no longer taken all seven days as in the Temple, was retained only on the seventh day as a remembrance of the Temple, with the hakafot and the recitation of Ana Hashem preserved as a prophetic institution (Mishneh Torah, Shofar, Sukkah and Lulav 7:22-23), a continuity also traced by Rav Eliezer Melamed (Peninei Halakhah, Sukkot 6:2).
The Tur and Shulchan Arukh describe the day's distinctive practices — reciting many psalms as on Yom Tov, lighting extra candles, loosening the lulav's binding, circling seven times, and taking the aravah as a remembrance of the Temple — tying these to the idea that on Sukkot the world is judged concerning water and that the judgment's seal is finalized on this day (Tur, Orach Chayim 664, Shulchan Arukh, Orach Chayim 664:1-3), with the Mishnah Berurah and Arukh HaShulchan elaborating the same Temple-remembrance rationale for the aravah and hakafot (Mishnah Berurah 664:1-20, Arukh HaShulchan, Orach Chaim 664:1-10, Chayyei Adam, Shabbat and Festivals 148:19, Levush, Orach Chayim 664:3).
Later authorities deepen the day's significance as the final point of judgment: Rav Eliezer Melamed (Peninei Halakhah, Sukkot 6:1) cites the Zohar's teaching that there are three times of judgment—Rosh Hashanah, Yom Kippur, and Hoshana Rabbah—when the verdict is carried out, and Kitzur Shulchan Arukh Yalkut Yosef, Orach Chaim 664:1 likewise describes it as the last of the days given for repentance before the notes of judgment are delivered, a theme Michtav MeEliyahu (Rav Dessler) frames as the culmination of the teshuva accomplished through sukkah and lulav.
Kabbalistic sources locate the day's character in the cosmic process of judgment reaching completion: the Zohar as rendered by Sulam on Zohar, Tzav 114:1 describes the seventh day as when the judgments of the world are concluded and the hakafot draw down water-blessing through the aravot, while Sulam on Zohar, Tzav 113:1-2 explains that the seven days of Sukkot require actual deeds rather than mere speech to draw down the same spiritual influence, and Menorat HaMaor and Kad HaKemach, Willow 1:1 likewise link the day to the sealing of judgment over water and the mystical significance of the name Hoshana Rabbah itself.
Chassidic teaching, as in Sefat Emet, Devarim, Sukkot 19:9 and Sefat Emet, Devarim, Sukkot 18:9, reads the aravah's lack of taste and fragrance as symbolizing the lowliness through which even the humblest are saved on this day, invoking the phrase "dalusi veli yehoshia" to explain why the day is called Hoshana Rabbah.
Rav Gavriel Zinner (הושענות) describes the practical Hoshana Rabbah customs as direct commemorations of the Temple service: taking a separate aravah, circling the bimah seven times with the Hoshanot, bringing out the Torah scrolls, and striking the aravot, while Rav Gavriel Zinner (ליל הושענא רבה) describes the night itself as a solemn 'night of sealing' marked by wakefulness, Torah study, Tehillim, and careful conduct.
Rav Ephraim Greenblatt (Revavos Ephraim 5:415) traces the name itself to the Gemara and Mishnah period, noting that Hoshana was recited daily during the hakafot with the lulav, and that on the seventh day the sevenfold circling with many Hoshana piyutim led Rashi, Tosafot, and other early authorities to call the day Hoshana Rabbah.
The broader pilgrimage context of Sukkot as a time of judgment over rain is reflected in Zechariah 14:16-19, which ties the nations' observance of the festival to receiving rain, while the thirteen attributes of mercy invoked in repentance generally, as discussed in Rosh Hashanah 17b:5-7, and the law of sukkah's day-and-night obligation in Sukkah 43b:1 and the dispute over the palm branches at the altar in Sukkah 45b:8-9, round out the Talmudic background for the day's practices, alongside the Zohar's description of communal joy and acceptance in Zohar, Tzav 19:134.